Analyzing samples representative of downhole fluids is an important aspect of determining the quality and economic value of a hydrocarbon or water producing formation.
Present day operations obtain an analysis of downhole fluids usually through wireline logging using a formation tester such as the MDT™ tool of Schlumberger Oilfield Services. However, more recently, it was suggested to analyze downhole fluids either through sensors permanently or quasi-permanently installed in a wellbore or through sensor systems mounted on a drillstring. The latter method, if successful implemented, has the advantage of obtaining data while drilling, whereas the former installation could be part of a control system for wellbores and hydrocarbon production, therefrom.
To obtain first estimates of the composition of downhole fluids, the current MDT™ tool uses an optical probe to estimate the amount of hydrocarbons in the samples collected from the formation. Other known sensors use resistivity measurements to discern various components of the formations fluid.
To meet demand for chemical measurements of increasing accuracy, it may appear obvious to adapt chemical analysis tools known from chemical laboratory practice to the hostile environment of a subterranean borehole. Such known analysis tools include for example the various types of chromatography, electrochemical and spectral analysis. However, a closer look at the environmental conditions within a subterranean wellbore lets those attempts appear as futile.
Various types of downhole measurement tools are known. Examples of such tools are found in the U.S. Pat. Nos. 6,023,340; 5,517,024; and 5,351,532 or in the International Patent Application WO 99/00575.
It is therefore an object of the present invention to provide apparatus and methods that would allow the use of chemical analysis tools known per se in a subterranean wellbore.